Prediction of the flash point of ternary ideal mixtures

Transcription

1 Electronc Journal of New Materals, Energy and Envronment Volume No. (25), -5 url: eissn: redcton of the flash pont of ternary deal mxtures M. Hrstova Unversty of Chemcal Technology and Metallurgy, 8 Kl. Ohrdsk Blvd., 756, Sofa, Bulgara E-mal: marana_hrstova@abv.bg Abstract The flash ponts of three organc ternary mxtures were measured n the present work. The expermental data was obtaned usng the ensky-martens closed cup tester. The expermental data were compared wth the values calculated by the Law s model by the applcaton of Raoult s law. The predcton results can be appled for nherently safer desgn for chemcal processes. Keywords: flash pont, ternary deal mxture, predcton, ensky-martens closed cup tester. Introducton One of the most mportant physcochemcal propertes for establshng the potental for fre and exploson of a hazardous substances and mxtures s ts flash pont (F). The F s related to the vapor pressure of a flammable lqud and s defned as the lowest temperature at whch t can form a combustble mxture wth ar []. Knowledge of the flash ponts s mportant for classfcaton of materals accordng to the classes defned n each partcular regulaton [2,3] and has great practcal sgnfcance n handlng, transport, storage and packagng of these materals. Flash ponts are determned expermentally by heatng the lqud n a contaner and then ntroducng a small flame just above the lqud surface. The temperature at whch there s a flash/gnton s recorded as the flash pont. Two general methods are called closed-cup and open-cup [4,5]. The closed-cup method prevents vapors from escapng and therefore usually results n a flash pont that s a few degrees lower than n an open cup. Because the two methods gve dfferent results, one must always lst the testng method when lstng the flash pont. Flash ponts of common pure chemcal substances are wdely reported, but very lmted data are avalable for mxtures. Ths fact may explan the decson of the EC (European communty) CL (Classfcaton, Labelng, and ackagng) [3] to delay the classfcaton of mxtures untl 25. Snce the expermental measurement of flash pont s expensve and tme consumng, predctve theoretcal methods are requred to estmate the flash ponts of both pure components and mxtures. Several predcton models are presented n the lterature for the predcton of mxture flash pont [6-]. Law et al. [2-6] have reported a seres of models, whch could be used for predctng the flash ponts for deal and non deal solutons. The basc assumpton n these models s that the lqud phase s n equlbrum wth the vapor. The purpose of ths study was to measure and predct the flash pont of ternary deal mxtures. The flash ponts were measured by ensky-martens closed cup tester, and compared wth the values calculated by usng Law s model and Raoult s law. RECEIVED: MARCH 5.25 AVAILABLE ONLINE: MARCH 5.25 COYRIGHT 25, ACADEMIA SERDICA ACTA LTD.

2 M. Hrstova / EJNMEE Experment The expermental data was obtaned usng the ensky-martens closed cup tester. The closed cup tester was operated accordng to the standard test method, EN ISO 279 [7]. The ambent barometrc pressure was observed and recorded at the tme of the test. When the pressure dffered from 76 mm Hg (.3 ka), the flash pont was corrected as follows: Corrected flash pont = T +.25(.3 ) where T s the observed flash pont (ºC); s barometrc pressure (ka). The mole fracton of each component was determned by measurng the mass usng a Sartorus dgtal balance (senstvty. g, maxmum load g). The sample was not strred whle the flame was lowered nto the cup. The flash pont was the temperature at whch the test flame applcaton caused a dstnct flash n the nteror of the cup. The measured value was the mean of two measurements whch do not dffer by more than 2ºC. 3. Mathematcal model for predctng the flash ponts of mscble deal mxtures Le Chateler s rule [8] for a flammable mxture of vapor + ar can be expressed as y LFL where y s the vapor phase composton of a flammable substance and LFL s the lower flammable lmt of the pure component. The LFL s expressed n relaton to the pure component vapor pressure at ts F,, as LFL, F (), (2) where s the ambent pressure. The flash pont of a substance s generally measured under atmosphere pressure. Under ths condton the vapor phase usually exhbts an deal behavor. In the case of a lqud mxture contanng flammable substances, the vapor lqud equlbrum of component s gven by where γ s the lqud phase actvty coeffcent. Substtutng Eqs. (2) and (3) nto Eq. () [9]: y x (3) x, (4) The vapor pressure for a pure substance s a functon of temperature and can be estmated by the Antone equaton: B log A (5) T C, The vapor pressure of pure lqud at ts flash pont, as presented n Eq. (4), can be estmated by substtutng T,, the flash pont of component, nto the Antone equaton. For an deal lqud mxture the actvty coeffcents of all components are equal to one, so Eq. (4) can be reduced to a smpler form, x, (6) For a ternary lqud soluton, Eq. (6) reduces to x, x 2 2 2, x 3 3 3, (7) - -

3 M. Hrstova / EJNMEE 25 Therefore, the reduced model for the flash pont-predcton under an deal soluton assumpton can be descrbed usng Eqs. (5) and (7). Table. Flash ponts and Antone coeffcents for pure components Substance CAS Flash pont [ C] Antone coeffcents* A B C * Heptane , ,37 26,636 Octane , ,82 26,385 Nonane , ,46 2,82 Dodecane , ,27 8,835 Benzene , ,76 29,6 Toluene , ,3 29,87 p-xylene , ,43 25,3 log ( ) B mmhg A T ( C ) C Three groups of ternary mxtures were selected to determne the expermental flash pont values. Accordng to the mathematcal model, the flash pont can also be obtaned usng calculatons. The measured flash ponts of studed ternary mxtures and the predcted by Law s model are presented n tables 2-4 respectvely, where T T T. exp ermental predcted Fgures -3 dsplay the predctve curves smulated by the model under an deal soluton assumpton. Table 2. Expermental flash ponts and predctons for heptane () + nonane (2) + dodecane (3) mxture X X 2 X 3 Exp. ( C) redct. ( C) C T,,,8 66, 64,5,5,,4,5 49,5 48,9,6,,6,3 4,5 39,6,9,2,5,3 34,5 35,5,,2,7, 26, 27,2,,5,2,3 25, 23,5,5,5,4, 5,5 6,,5,6,,3 2,5 9,6,9,7,,2,8 2,3,5,7,2, 9,5 8,9,6-2 -

4 M. Hrstova / EJNMEE 25 Mxture Contour lot of Fp (component amounts) Heptane Fp < > 8 Nonane Dodecane Fg.. Flash pont predcton results for mxture of heptane + nonane + dodecane Table 3. Expermental flash ponts and predctons for octane () + nonane (2) + dodecane (3) mxture X X 2 X 3 Exp. ( C) redct. ( C) C T,,2,7 6,5 6,7,2,,4,5 52,8 5,4,4,,5,4 48, 46,6,4,,8, 34, 33,3,7,2,2,6 56,5 54,5 2,,2,5,3 42,5 4,2 2,3,2,7, 3,5 3,6,,4,,5 46, 45,7,3,4,4,2 34,5 32,3,2,5,3,2 32,5 3,6,9 Mxture Contour lot of Fp (component amounts) Octane Fp < > 8 Nonane Dodecane Fg.2. Flash pont predcton results for mxture of octane + nonane + dodecane - 3 -

5 M. Hrstova / EJNMEE 25 Table 4. Expermental flash ponts and predctons for benzene () + toluene (2) + p-xylene (3) mxture X X 2 X 3 Exp. ( C) redct. ( C) C T,,2,8 2,5 9, 2,4,,5,75 9,8 8,2,6,,2,7 6,9 7,2,3,,5,4 3,,5,5,5,,75 8,5 7,2,3,2,,7 7, 5,4,6,2,3,5 3,,6,4,3,,6 3,5,7,8,3,3,4 9,5 7,9,6,35,,55, 9,8,2 Mxture Contour lot of Fp (component amounts) Benzene Fp < > 2 Toluene Xylene Fg.3. Flash pont predcton results for mxture of benzene + toluene + p-xylene The maxmum absolute devaton between the model and the expermental results s 2,4 C. The average absolute devaton s, C for heptane + nonane + dodecane mxture,,35 C for the octane+nonane+dodecane, and,47 C for benzene+toluene+p-xylene mxture. The model calculaton results are n a good agreement wth the expermental results, and, therefore, the model has good predctablty and applcablty. In the predcton model, t was assumed that the vapour phase and lqud phase of a soluton are n equlbrum. The predcted data was only adequate for the data determned by the closed cup test method, and may not be approprate to apply to the data obtaned from the open cup test method because of ts condton of havng devated from the vapour-lqud equlbrum. 5. Concluson The flash ponts of three ternary mxtures were measured by ensky-martens closed cup tester. The expermental data were compared wth values calculated by usng Law`s reduced model for the predcton of a soluton s flash-pont value for an assumed deal soluton. The model descrbed n ths paper s able accurately to predct the flash pont of a ternary deal solutons as revealed by a comparson between predcted and expermentally-derved data. The predcton results of ths model can be appled for nherently safer desgn for chemcal processes, such as the determnaton of the safe storage condtons for flammable solutons

6 M. Hrstova / EJNMEE 25 Estmaton of ternary mxture flash pont s very useful for the assessment of flammablty hazards, because t saves tme and effort. References [] Crowl D.A, Louvar J.F. Chemcal rocess Safety: fundamentals wth applcatons. 2nd ed. Upper Saddle Rver: rentce Hall TR; 22 [2] Regulaton (EC) No 97/26 of the European arlament and of the Councl concernng the Regstraton, Evaluaton, Authorzaton and Restrcton of Chemcals (REACH) [3] Regulaton (EC) No 97/26 of the European arlament and of the Councl concernng the Regstraton, Evaluaton, Authorzaton and Restrcton of Chemcals (REACH) [4] Amercan Socety for Testng and Materals, ASTM E 52-84: Selecton and Use of ASTM Standards for the Determnaton of Flash ont of Chemcals by Closed Cup Methods (ASTM Internatonal, West Conshohocken, A, 2) [5] Amercan Socety for Testng and Materals, ASTM 3: Standard Test Method for Flash ont and Fre ont of Lquds by Tag Open-Cup Apparatus (ASTM Internatonal, West Conshohocken, A, 2) [6] R.O. Wckey, D.H. Chttenden, Hydrocarb. rocess, 963, 42(6), [7] L. Catore, V. Naudet, J.hys.Chem.Ref.Data, 24, 33, 4, 83-, [8] L. Catore, S. aulmer, J. hys. Chem.Ref. Data, 26, 35,, 9-4 [9] J.L. McGovern, J. Coats Technol., 992, 64, 8, [] W.A. Affens, G.W. McLaren, J. Chem. Eng. Data, 972, 7, [] D. Whte, C.L. Beyler, C. Fulper, J. Leonard, Fre Saf. J., 997,28, -3 [2] H.-J. Law, Y.H. Lee, C.L. Tang, H.H. Hsu, J.H. Lu, J. Loss rev. rocess Ind., 22, 5, [3] H.-J. Law, Y.Y. Chu, J. Hazard. Mater., 23,, 83-6 [4] H.-J. Law, Y.Y. Chu, J. Hazard. Mater., 26, 37, [5] H.-J. Law, Y.H. Lee, Chen-Tsun, V.Gerbaud, Chem. Eng. Sc., 28, 63, [6] H.-J. Law, Y.H. Lee, V. Gerbaud, Y.H. L, Flud hase Equlb., 2, 3, 7-82 [7] EN ISO 279. Standard Test Methods for Flash ont by ensky-martens Closed Cup Tester [8] Le Chateler, H., Ann.Mnes, 9, 89, , [9] Law H-J, Tang C-L, La J-S.,Combust Flame 24,38,